Interpretation ID: nht78-2.25

DATE: 03/20/78

FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA

TO: General Cable Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of February 3, 1978, concerning placement of the rear identification lamps on a truck. Because the truck has a mast assembly located on the longitudinal axis of the vehicle and center of the rear axle, you have asked whether the lamps should be mounted "on the mast as high as possible or on the rear face of the rear floor decking."

Table II of Federal Motor Vehicle Safety Standard No. 108 requires rear identification lamps to be mounted "as close as practicable to the top of the vehicle. . . ." If placement on the mast interferes with the operation of the lift, or if the lamp would be easily damaged in that location, that location would not appear to be "practicable" within the meaning of Standard No. 108, and the deck location would fulfill the practicability requirements.

You have also asked which is more important in locating identification lamps: "(1) . . . as high as possible on a stationary surface and face the lights toward the rear, or (2) to locate to the most rearward surface and then as high as possible on that surface". Your first choice is the correct one. The purpose of the three lamp cluster is to identify large and frequently slow moving vehicles under conditions of reduced visibility. Therefore, it is more important for the lamps to be located high than it is for them to be at the rear end of the vehicle, for example, on the cab rather than at the deck end. However, the decision as to what is "practicable" is initially that of the manufacturer and we have generally found those decisions to be correct.

SINCERELY,

General Cable

February 3, 1978

Department of Transportation c/o Bradley E. Marks

Dear Mr. Marks:

We, at General Cable, primarily design and manufacture vehicles with aerial lifts for personnel to service electrical utilities. For this type of equipment, we seem to have a problem truly defining a section of F.M.V.S.S.108 for our application.

The particular section in question is the location of the rear identification lights.

Since we design a lift whose mast assembly is located approximately on the longitudinal axis of the truck and centerline of the rear axle, should we mount the cluster of lamps on the mast as high as possible, or on the rear face of the rear floor decking? The definition of the exact location is rather vague for our industry.

Also, Mr. Marks, we have a secondary problem. Standardization of the lighting location. This mast assembly may, at some time in the future, be located further forward, just behind the truck cab. This would require the turret, boom, boom rest and basket to be positioned towards the rear of the vehicle.

The way I've interpreted the law for this particular configuration would have us locating the cluster of lights on the rear face of the rear floor decking. This due in part to the photometric interference from the basket and/or boom and boom rest assemblies.

At this point in time I must now ask, which is more important in locating these lights: (1) to locate as high as possible on a stationary surface and face the lights towards the rear? or (2) to locate to the most rearward surface and then as high as possible on that surface?

We would like a ruling on this matter as soon as possible as production of this unit is scheduled within the coming weeks.

Thank you very much, Mr. Marks, for your co-operation in this matter. Any response to this problem may be addressed either to myself or my superior, Mr. Bill Hensley, Chief Engineer.

Garry Williams Body Designer Telsta Group

cc: Bill Hensley; Van Walbridge